Abstract This is an application for a K23 Mentored Research Career Development Award for Dr. James Chen, an Assistant Professor and Orthodontist at UCSF. Dr. Chen is working to establish his research on early interceptive orthodontic treatment for socially disadvantaged children and his clinical expertise. This application is designed to provide the necessary mentoring, training, and research support Dr. Chen needs to become a successful independent investigator. Specifically, this award sets out to accomplish the following goals: (1) become an expert in patient-based early interceptive orthodontic treatment research; (2) to determine the equivalence in treatment outcome and child self-perception between a removable-appliance-based protocol and a fixed-appliance-based protocol; (3) to learn and implement advanced biostatistical methods in clinical research; (4) to learn and implement cost-effectiveness analysis models on early interceptive orthodontic treatment protocols; (5) to develop and grow a strong independent clinical research career; (6) to be a leader in access to orthodontic health care in the United States. In order for Dr. Chen to achieve these goals he will need support to design and implement his study. Dr. Chen has assembled a diverse mentoring team comprised of a primary mentor, Dr. George Taylor, who is the Department Chair of Preventive and Restorative Sciences and conducts public-health-related research on diabetes and periodontitis, and three co-mentors with one consultant: Dr. Greg Huang, Chair of Orthodontics at the University of Washington, who is an expert on evidenced based orthodontic research; Dr. James Kahn, Professor of Clinical Epidemiology in Medicine at UCSF, who is an expert on cost-effectiveness analysis and health care economics; Dr. Jing Cheng, Associate Professor in the School of Dentistry, who is an expert on study design and biostatistical analysis; and Dr. Gerald Nelson, Acting Chair of Division of Orthodontics at UCSF, will serve as a clinical consultant because of his extensive knowledge and experience with early interceptive orthodontic treatment. Oral health disparities and access to orthodontic care for socially disadvantaged children is a major concern in the United States. Dr. Chen's research will focus on critically analyzing a novel removable appliance based treatment protocol aimed at reducing orthodontic need while limiting the financial impact on low-income families compared to the existing fixed appliance based treatment protocol. The hypothesis of this study is that a treatment protocol based on using removable appliances provides the same treatment outcome but better cost-effectiveness than a traditional fixed-appliance protocol. The crux of this study will include comparing the differences in treatment outcome (AIM 1), measured by occlusal index scores (PAR Index and ICON Index), the differences in child self-perception measured by Child Perception Questionnaire (AIM 2) after orthodontic treatment, and the difference in cost-effectiveness (AIM 3) between the removable appliance only group and the fixed appliances only group. For all three aims, Dr. Chen will recruit participants beginning early interceptive orthodontic treatment at La Clinica Community Clinic and UCSF Orthodontic Residency Clinic and he will follow them to completion of their orthodontic treatment and then progression into full permanent dentition. This study will require sophisticated multiple linear regression analyses. This research will be the starting point for developing and initiating a large intervention trial comparing removable based appliance therapy to fixed appliance based therapy for socially disadvantaged children. Towards the end of this K23 award Dr. Chen will prepare and apply for a R34 award to develop the intervention trial followed by an application for an U01 clinical trial award.